Rehabilitation and maintenance of buildings - 01

1. Rehabilitation and maintenance of buildings - 01 Karel Mikeš

2. References • Errors in the design of structures and modern reconstruction • Mechanical properties of cast iron, mild iron and steel at historical structures • Causes and analysis of steel structural failures • Assessment of load bearing structures and reasons for refurbishment of steel structures • Overview of codes for design and actions on structures • Inspections and material testing • Introduction of basic methods of reinforcing steel • Strengthening of individual members subjected to axial load (tension, compression) – elastic and plastic check procedures •  Strengthening of individual members subjected to bending • Strengthening of individual members subjected to combination of effects – elastic and plastic check procedures • Strengthening of riveted/bolted/welded connections • Repair and reconstruction of civil structures

3. References • Agócs Z., Ziolko J., Vičan J., Brodniansky J.: Assessment and Refurbishment of Steel Structures, Spon Press, 2005. • Mazzolani F.: Refurbishment by steelwork, ArcelorMittal, Luxembourg Spal L.: Refurbishment of Steel Structures, SNTL, Praha, 1968. • Vašek M.: Strengthening of steel structures, DOS T 3, No. 04, ČKAIT, 2000 • Háša P., Jeřábek L., Rosenkranz B., Vašek M.: Collapse of boiler house roof of the power station in Opatovice, Konstrukce No.3, 2004

4. Contents • Properties of material • Failures of steel structures • Types of refurbishment • Methods of reliability verification • Basis of design of steel structures • Assessment of steel structures • Strengthening of members • Strengthening and refurbishment of structures • Refurbishment of masonry structures using steelwork • Seismic upgrading using steel structure

5. Properties of material • Cast iron • Wrought iron • since 1785 • until 1892 – 1905 • after 1905 only exceptionally • Mild steel • since 1905

6. Cast iron • Fragile • Suitable for compression, worse for bending • High contents of C (2,1%) • Mechanical properties: • E ~ 100 000 MPa (N/mm2) • fu ~ 120 ÷ 140 MPa

7. Wrought iron • Production • Temperature  1000oC  doughy state • Low charge – 200-600 kg • Mechanical reduction of undesirable elements  • Large scatter of mechanical properties • Layered anisotropic structure • Local defects

8. Wrought iron • Chemical composition • Large scatter • Lower contents of C • High contents of P (phosphorus) – could be problem • Problems • Uncertain weldeability • Low strength through thickness  Lamelar tearing

9. Wrought iron • Mechanical properties in rolling direction • E = 180 000 ÷ 200 000 MPa (N/mm2) • fy ~ 230 MPa (mean) • fu ~ 340 ÷ 370 MPa • Lower ductility but still sufficient

10. Mild steel • Production • Liquid state • Larger charges • Since 1905 properties similar to present steel • E = 210 000 MPa • fy , fu similar to present S235 (Fe360)

11. Properties of material • Time of construction  Type of material • How to determine: • from documentation (rarely) verification by tests is recommended • using tests • Mechanical properties of iron/steel are NOT time depending(except fatigue)

12. Contents • Properties of material • Failures of steel structures • Types of refurbishment • Methods of reliability verification • Basis of design of steel structures • Assessment of steel structures • Strengthening of members • Strengthening and refurbishment of structures • Refurbishment of masonry structures using steelwork • Seismic upgrading using steel structure

13. Causes of failures of steel structures - phases • Errors in design • Fabrication, erection • Operation • corrosion • fatigue • high temperature • Additional temperature loading • Fire • accidental events

14. Causes of failures of steel structures - phenomenons • Underestimation of loading • Discrepancy of model and reality • Defective or inadequate material • Stability of compression members (or beams) • Stability of plates • Brittle fracture • Weak joints • Aerodynamics • Fatigue • Typically Failure = more than one cause

15. Causes of failures of steel structures - phenomenons Discrepancy of model and reality • Wrong selection of details, not correspondng to assumption (fixed/hinged) • Unconsidered eccentricity in joints • Different load application points • Omitted effects (torsion, secondary moments) • Non-considered reduction of cross-section

16. Tay bridge 1879 • Underestimation of load: wind load not considered • Bad material: piers – cast iron, bracing – wrought iron with slag • Train speed 60 km/h instead of 40 km/h

17. Tay bridge 1879 • Collapse in wind storm with train • 75 died

18. St. Lawrence, Quebec 1907 • Flexural buckling of compression member • Underestimation of dead load • Errors in the design of joints

19. St. Lawrence, Quebec 1907 • Collapse in construction stage • 86 died

20. Hasselt 1937 • Brittle fracture • Bad selection of steel • Wrong welding process  large residual stresses

21. Hasselt 1937 • Collapse when tram crossed

22. Tacoma Narrows 1940 • Aerodynamics • Suspension bridge, span 853 m • New bridge in 1950 • Nowadays 2 bridges (2007)

23. Tacoma NarrowsAssembly 24

24. Collapse http://www.youtube.com/watch?v=AsCBK-fRNRk http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_Collapse 25

25. Collapse due to plate buckling • Vienna 1968 • Milford Haven (Wales) 1970 • West Gate Bridge (Melbourne) 1970 • 35 died • Koblenz (Germany) 1971 • Extensive research in 1970‘s • New codes with new procedures

26. Milford Haven (Wales) 1970 • Eccentric load of diaphragm • Imperfections • Insufficient stiffening of diaphragm  capacity  50% of actions • 4 died

27. Koblenz 1971 • Buckling of unstiffened plate • 9 died

28. Failure of roof at Opatovice power station • Structure from 1957 • Main frame: fixed columns + truss girder, 27,5 m span • Collapse: 11/2002 • during reconstruction of roof • snow load • Original documentation: • Just part was found • Calculations missing

29. Failure of roof at Opatovice power station

30. Failure of roof at Opatovice power stationCauses • Overloading by dead load • Additional layers of concrete, water-proofing layers • Originally under-dimensioned structure • Very poor quality of welds • Not-functional dilatation detail • collapse of whole roof

31. Contents • Properties of material • Failures of steel structures • Types of refurbishment • Methods of reliability verification • Basis of design of steel structures • Assessment of steel structures • Strengthening of members • Strengthening and refurbishment of structures • Refurbishment of masonry structures using steelwork • Seismic upgrading using steel structure

32. Reasons for refurbishment of steel structures • Malfunction of structure • Need of change • Increased loading • Bridges • Buildings • Change of use • Need of free space • Bridges – new clear profile • Other reasons, e.g.: • local situation (neighbour buildings) • war

33. Types of refurbishment • Strengthening • Strengthening/enlargement of elements/joints • Change of static scheme • Prestressing • Coupling with concrete • Indirect strengthening • Restoration/Repair • Replacement • Extension • Utilization of reserve of structure

34. Utilization of capacity reserves of structure • Detection and improvement of loading • Pernament loading • Climatic loading • Service loading • Real material properties • More precise calculation

35. Utilization of capacity reserves of structureMaterial properties • Tensile tests • Real fy, fu • Plastic reserve • Bi-linear stress-strain relation • MNA – plastic hinges

36. Utilization of capacity reserves of structureMore precise calculation • Calculation in accordance with • present knowledge • present (valid) codes • 3D complex models • Shell elements • Joints • Shell structures (silos, pipelines ...) • Interaction of elements • Connections • Semi-rigid connections – new standards enable to determine joint stiffness • Column bases • Stochastic methods of the reliability verification